The present invention relates broadly to a phase shifter apparatus, and in particular to a low pass T-section digital phase shifter apparatus.
In the prior art, many electronic devices such as, for example, phased array systems utilize fundamental phase shifting circuits to achieve important functions. According to well-known prior art designs, phase shifters devices have generally required the use of circuits which employed a number of inductive elements. These prior art discrete element circuits are expensive since they must be built up element by element and to this date, it was not possible to implement an inductor into a monolithic or similar type circuit. In addition, the inductors which are rather expensive, add to the overall circuit cost.
Other prior art phase shifters have been developed to utilize digital techniques in obtaining the phase shift. However, the digital phase shifters in general are even more expensive than the discrete element inductive phase circuits, but they do have the distinct advantage of being mathematically predictable and are susceptible to monolithic implementation as well as batch processing.
At present, it is clear that none of the prior art phase shifters are able to satisfy the dual requirements of economy and small size. Therefore, it would be particularly desireable if such a circuit could be developed, particularly if such a circuit would be susceptible to a monolithic implementation capable such that it would be capable of being produced at low cost in large quantities.
In the military market, there is an increasing demand to design low loss phase shifters at especially extra high frequencies (EHF). The circuit losses are basically due to switching elements as well as mismatch and passive circuit components. Losses may be reduced by choosing the monolithic approach since it provides compact size which in turn reduces the passive component losses. On the other hand, in many of the conventional design techniques, the mismatch losses are intrinsic to the design and they may not be suitable for monolithic realizations. In the academic environment while the study continues on the low-loss switching devices, different phase shifter circuit configurations which are suitable for monolithic implementation are also searched extensively.
In the prior art, there are new digital phase shifter configurations which are based upon the operation of high-pass L-C ladders as phase shifting units. These circuits provide relatively better phase shifting performance over the other conventional circuits. In the present invention, a complementary low pass L-C ladder T-section digital phase shifter which has outstanding phase shifting characteristics over the prior art high-pass T-section phase shifter is presented. Furthermore, the inductances utilized in the low pass phase shifter apparatus provide practical flexibility to make the circuit interconnections. Therefore, the new low pass T-section phase shifter apparatus will find wide application in the system design where conventional and other new approaches are not feasible to use.
In addition, the present invention is arranged in the form of a T-section digital phase shifter which has better insertion loss characteristics with improved phase tracking capability over the normal conventional approaches.